Pressure systems, such as breastmilk expression systems, have been disclosed that include mechanisms to selectively modify pressure within the system. For instance, U.S. Pat. No. 5,007,899 discloses a breastpump with a piston pump having an aperture in a piston cylinder. The breastpump exposes the vacuum generating chamber to atmosphere when the head of the piston passes beyond the aperture. This returns the chamber to ambient pressure and limits peak negative pressure.
U.S. Pat. No. 8,070,715 discloses a breastpump system having a solenoid valve provided in an ambient airline. The solenoid valve is operated by a controller to open when a vacuum in a breastshield of the breastpump system reaches a desired pressure, permitting the vacuum within the breastshield to decrease (in other words, permitting the pressure in the breastpump system to increase) toward ambient pressure. However, instead of allowing the vacuum to decrease all the way to ambient pressure, the breastpump is further provided with a regulator that closes during breastpump operation once the system reaches a preset minimum vacuum level.
The known pressure control mechanisms may require more than desired design complexity. For example, the piston-cylinder/aperture design may limit the overall performance of the system. The solenoid valve needs to be powered directly. The solenoid valve also adds cost to the system, and may generate undesirable noise in the system. For these and other reasons, previously-designed pressure control systems may introduce limitations for optimizing the design.